This invention relates to a yarn changing device in a flat-bed knitting machine, especially a hand-operated flat-bed knitting machine, and more particularly to a yarn changing device which has three or more yarn guides selectively shiftable to and from an operative position.
A knitting machine is customarily provided with a yarn changing device to facilitate the changing of the various yarn feeds, for example, for effecting multi-color or fairisle pattern knitting with the machine. A yarn changing device for use with a flat-bed knitting machine having a carriage mounted for slidable movement on the needle bed is conventionally disposed at one end of the needle bed and has three or more yarn guides each shiftable to and from an operative position to permit the associated yarn to be fed to the knitting needles. Each time it is necessary to change the particular knitting yarn, the associated yarn guide must be selectively brought into the operative position.
The fairisle knitting pattern in which the pattern of the fabric is knitted with a yarn of a given color against the background of the fabric with a yarn of a different color is a preferred fairisle pattern to be knitted on a flat-bed type knitting machine. In knitting such patterns on a flat-bed knitting machine the two yarn guides are conventionally, alternately brought to the operative position in response to each reciprocation of the carriage on the needle bed. The respective yarns are fed to knitting needles through a yarn carrier on the carriage when the yarn guides are in the operative position.
A still more attractive, modified form of fairisle knitting pattern is one in which the pattern and the background of the fabric includes at least three different colors and in which any complete course of stitches includes another color. This modified fairisle pattern requires yarns of at least three different colors. In knitting this modified fairisle pattern certain courses of stitches are knitted with two differently colored yarns which are alternately brought into the operative positive with each reciprocation of the carriage whereas certain other courses of stitches are knitted with one or the other of those two yarns and a third yarn. Accordingly a yarn changing device, especially for a hand-operated flat-bed knitting machine, is preferably constructed to successively select two out of the several yarn guides provided and to successively bring two yarn guides thus selected, alternately into the operative position, all in synchronism with the reciprocations of the carriage.
Swiss Pat. No. 387,858 discloses a yarn changing device having a construction similar to that just described which includes four slidable yarn guides, each provided with an abutment, and each being urged from the operative position by a spring. A drive shaft adapted to be driven by the carriage to rotate about its axis by an angle of 45.degree. is disposed transversely to the yarn guides. The drive shart has a pair of toothed wheels mounted for axial displacement thereon and for rotation integral therewith. Each wheel has four angularly equally spaced teeth for engagement with the abutments of the yarn guides and is disposed relative to the other wheel so that the teeth of a given wheel are displaced by an angle of 45.degree. relative to the teeth of the other wheel. Each wheel is manually displaceable along the axis of the drive shaft to permit alignment with and selection of a yarn guide. Thus, when the carriage is operated, the drive shaft is rotated as previously described and the selected yarn guide is engaged at the abutment thereof by a tooth of the wheel aligned therewith and is thereby slidably moved to the operative position against the urging of the spring. The yarn guide thus moved is held in the operative position until a subsequent rotation of the drive shaft causes the tooth of the wheel to move clear of the abutment of the yarn guide, thereby releasing the yarn guide. With this arrangement, alternate actuation is achieved for the two selected yarn guides into the operative position by the angular displacement of the teeth between the two wheels which are, in turn, equalized with the rotational angle of the drive shaft.
The yarn changing device of Swiss Pat. No. 387,858, however, is less than satisfactory in certain applications because, for example, the selection of a yarn, particularly a third yarn as described above, cannot always be performed with a simple operation of manually displacing a toothed wheel to the proper position. This difficulty exists because the movement of either toothed wheel on the shaft is dependent upon the other. For example, when a yarn guide on one side of the first selected yarn guide is to be newly selected in place of the previously selected yarn guide on the other side of the first, the toothed wheel then aligned with the first yarn guide must be displaced. Such a displacement, however, causes an undesirable release of the first yarn guide from the operative position in which it should preferably remain. Thus, it is seen that selection of a new yarn sometimes may require complicated operational steps which, in turn, may lead to errors.
A program-controlled yarn changing device apparently capable of providing various yarn changing sequences, including those just described, is disclosed in German Patent Application No. 2,357,938, laid open on May 28, 1975. That patent application discloses a yarn changing device actuatable by the carriage and including a control means using a conventional perforated program card as the program providing means and an overriding manually operable means for selecting the yarn guides independent of the program card. This device, however, is not well suited for knitting operations in which two selected yarns are alternately brought into operative position for feeding in response to the reciprocating movement of the carriage. The control means disclosed in German Patent Application No. 2,357,938 is unduly complicated for such an application and a specially prepared program card is required. Alternatively, the required yarn guides must be manually selected each time the carriage is slidably reciprocated on the needle bed. A less than satisfactory procedure.